Field of the Invention
The present invention relates to an X-ray generating apparatus applicable to, for example, medical equipment and non-destructive testing apparatus, and to a radiography system using the same.
Description of the Related Art
X-ray generating apparatus in general have a built-in X-ray generating tube as an X-ray source. The X-ray generating tube includes a vacuum container in which a cathode is mounted to one opening of an insulating tube and an anode is mounted to the other opening of the insulating tube. An electron emitting source is connected to the cathode, and the anode includes a target. The X-ray generating tube generates an X-ray by applying high voltage between the cathode and the anode, and irradiating the target with an electron beam that is emitted from the electron emitting source as a result of the voltage application.
As an example of the X-ray generating apparatus, in Japanese Patent Application Laid-Open No. 2009-43658, there is disclosed a structure in which the anode is fixed to a metal casing, which is a container of the X-ray generating apparatus, in a manner that makes an output opening of the metal casing and an output window of the X-ray generating tube concentric with each other. With the structure of Japanese Patent Application Laid-Open No. 2009-43658, an X-ray emitted from the output window is radiated to the outside of the X-ray generating apparatus. This structure is connected thermally and electrically from the target in the X-ray generating tube to an anode member, which holds the target, and further to the metal casing of the X-ray generating apparatus, thereby dissipating heat of the target, which has risen in temperature when irradiated with an electron beam.
In the X-ray generating apparatus structured as disclosed in Japanese Patent Application Laid-Open No. 2009-43658, other electronic energies than an X-ray that are generated from a collision between electrons and the target for X-ray irradiation are converted into heat, which is dissipated from the target via the anode member to the metal casing. On the other hand, an electron emitting portion of the electron emitting source that emits the electrons generates heat as well, and a part of the generated heat is dissipated to a cathode member, which is opposed to the anode member relative to the vacuum container. The rest of the generated heat is released to the anode member, which is in proximity to the electron emitting portion, and is dissipated to the metal casing via the anode member. Accordingly, the generated heat from the target and a part of the generated heat from the electron emitting portion are conducted along a heat conduction path for heat dissipation from the anode member to the metal casing, and there is a fear that heat is not dissipated from the target satisfactorily.
High temperature in the target due to insufficient target heat dissipation has a fear of causing damage to the target such as the peeling, melting, or evaporation of a target layer, or a crack in a support substrate, which can result in fluctuations or a drop in X-ray output.